1. Field of the Invention
The invention relates to crank case oil pan drain plugs for automobile engines or the like, and refers more specifically to an oil pan drain plug including sealing means operable between the drain plug and the oil pan, on removal of the drain plug to drain oil from the oil pan, to prevent leakage of oil from the oil pan about the threads between the opening through the oil pan and drain plug, until the threads of the oil pan and the drain plug are disengaged, whereby the plug may be removed without leakage of oil on the tools used in or person removing the plug.
2. Description of the Prior Art
In the past, to remove a drain plug from the oil pan of an automobile engine or the like when draining and changing engine oil, after placing an oil collection pan under the crank case to receive the old oil, a wrench has generally been utilized to loosen and initially unscrew a bolt-like drain plug. Oil pan drain plugs of the past, as shown best in FIGS. 1 and 2, have usually had a threaded stem 13 which in use extends into the oil pan through a threaded opening in the oil pan, and a head 15 which extends exteriorly of the oil pan, shaped to facilitate operational engagement of a wrench with the drain plug head. After the initial loosening of the plug, the plug was usually unthreaded by hand. The plug was removed and the engine oil drained into the pan.
With such structure and method of the past, after a few turns of the plug, the oil began to leak out of the oil pan around the threads in the oil pan opening and on the drain plug and onto the tools and/or person removing the drain plug. At the very least, leaking oil is a messy nuisance, and sometimes it is hot enough to cause serious burns.
Such leakage also encourages the person removing the drain plug to hurry to complete the unscrewing and removal of the drain plug from the oil pan. This hurrying often results in dropping of the drain plug into the oil collection pan, requiring a messy search for the drain plug in the pan of, possibly hot, oil after the oil has been drained out of the engine into the oil collection pan.
Prior drain plug art for crank case oil pans has sometimes addressed these problems and has provided a variety of structures and methods for removal of oil from a crank case when it is desired to change the oil which partially alleviate these problems.
Such structure is shown in U.S. Pat. Nos. 1,804,960 and 4,231,544, both of which show special valves in conjunction with the usual drain plug opening in a vehicle oil pan that prevent undesired leakage. Note, however, that both of these patents require a complete new drain plug which is complicated to manufacture in comparison to the usual prior art drain plug 11 and is therefore expensive. Also, both of these drain plugs have operative parts extending below the engine oil pan which are subject to damage during use of the vehicle. In addition, they require the installation of an exteriorally threaded cylinder into the usually interiorally threaded opening in the crank case oil pan, which cylinder typically extends upward into the oil pan, thereby prohibiting the complete drainage of the old oil.
Other such structure is shown in the U.S. Pat. Nos. 5,299,777 and 5,326,071. These patents again teach drain plugs and methods which utilize the existing oil pan drain opening. However, both of these structures require special tools to actuate to permit draining of crank case oil. Also, they are again relatively complicated and therefore expensive.
Additional prior art structure is shown in U.S. Pat. Nos. 3,097,663 and 3,869,391. These patents do not prevent leakage as the drain plug is loosened to permit drainage of crank case oil from the oil pan, and both appear to require installation with the crank case oil pan at the time the pan is manufactured. They are again relatively complicated and therefore expensive to manufacture.
Thus, prior art has recognized the problem of leakage during drainage of oil from a crank case (see especially Pat. No. 5,326,071), and some have provided structures which will prevent messy leakage around a drain plug while it is being removed to drain oil from the crank case. However, such structures and methods of the past as shown in the patents listed above are complicated, so are expensive to produce. Further, in some instances, the prior art structures extend below the crank case oil pan by which they are carried, and are thus subject to damage, or require original equipment installation with the crank case oil pan and therefore are not suitable for aftermarket sales, or extend into the crank case oil pan resulting in incomplete drainage.